Structure of cationic surfactant micelles from molecular simulations of self-assembly

Abstract

Molecular dynamics simulations of self-assembly of n-decyltrimethylammonium bromide surfactants were performed using an atomistic model, and a detailed analysis of the spontaneously formed micellar aggregates was carried out. This allowed for a detailed study of the structure of cationic surfactant micelles free from any a priori assumptions regarding their size and shape. Atomic radial distribution functions, radial density profiles and bivariate water orientation distributions were computed. Together, they show the presence of a dry micelle core, with a hydrophobic environment similar to a liquid alkane, a well-defined head-group layer at the interface, and an outer layer of strongly bound bromide counterions. Water molecules penetrate the micelle as far as the innermost head site, adopting a sequence of orientations that is akin to that observed at planar interfaces with vapor or immiscible organic solvents. Water molecules at ACCEPTED MANUSCRIPT 2 the exterior of the micelle are highly polarized by the electrical double-layer formed by cationic head-groups and bromide anions, orienting themselves with their dipole vector pointing towards the micelle core.

Mechanism of Hydrotropic Action of Hydrotrope Sodium Cumene Sulfonate on the Solubility of Di-t-Butyl-Methane: A Molecular Dynamics Simulation Study

“…It is noticed that the difference between the actual and normalized or expected coordination number is small for below MHC concentration, and this difference begins to rise from the MHC region. These findings suggest more and more dehydration of hydrophobic tails of both SCS and DTBM molecules as SCS concentration increases, and this is quite similar to the behavior of classical surfactant in solutions above its CMC value. − For example, the results of a wide Q-range neutron diffraction measurement study and empirical potential structure refinement (EPSR) modeling of aqueous solution of surfactant decyltrimethylammonimum bromide (C 10 TAB) also showed that the hydrophobic tail groups of the surfactant orient themselves to minimize the contact with the solvent water molecules, and they form a hydrophobic core upon micellization . In this context we would also like to mention that neutron diffraction scattering experiments are also useful to study the aggregation propensity of solutes of different sizes including biomolecules. − For example, by using neutron diffraction with isotropic substitution (NDIS) experiment, Philip et al examined the aggregation tendency of pyridine molecules in aqueous solution that showed preferential exclusion of water molecules with increasing pyridine concentration .…”

Atomistic Structure of a Micelle in Solution Determined by Wide Q-Range Neutron Diffraction

“…Our findings support the very detailed analysis of ref. 50 and we conclude that the bromide ions do not penetrate into the micelle significantly beyond the CT group.…”

Modeling Self-Assembly of Silica/Surfactant Mesostructures in the Templated Synthesis of Nanoporous Solids

“…Recently, our group has used a different approach, based on atomistic molecular dynamics (MD) simulations of the initial stages of PMS synthesis [14,15]. The surfactant model was first validated by carrying out simulations of surfactant/water solutions [16,17]. Subsequently, several PMS synthesis solutions, including silicates, surfactants, water and counterions, and representing different stages of the synthesis process, were carried out.…”

“…Recently, our group has used a different approach, based on atomistic molecular dynamics (MD) simulations of the initial stages of PMS synthesis. , The surfactant model was first validated by carrying out simulations of surfactant/water solutions. , Subsequently, several PMS synthesis solutions, including silicates, surfactants, water and counterions, and representing different stages of the synthesis process, were carried out. It was demonstrated that silica monomers (monosilicic acid molecules) adsorb strongly on the surface of the micelles, replacing bromide counterions, and promote the growth of initially small spherical aggregates .…”